1. Field of the Invention
This invention relates to a device and method for dispensing aerosol sprays in a manner which promotes rapid and consistent vaporization. In particular, the invention relates to dispensing aromas.
2. Background
There are various known techniques for dispensing or dispersing aromas or olfactory stimulants. For example, aromatic oils are often dispersed by application of heat to an evaporation surface. The heat may, however, detrimentally affect the aroma being dispensed. As well, where the aroma dispensing device comprises an aromatic candle, the vapors carrying the aroma are often denatured or oxidized in the candle flame, reducing the intrinsic or “natural” quality of the fragrance. Other aroma dispensing devices rely on the use of propellants or aerosols to enable the dispersion. However, such propellants and aerosols may also detrimentally affect the aroma being dispersed.
In the conventional aroma delivery devices described above, it is difficult to consistently and precisely control delivery of the sprayed material. For example, in the case of an aromatic candle or other aroma delivery device that operates by using heat causing evaporation, some degree of evaporation will continue after the candle has been blown out or the device has been switched off. In addition, such devices generate an aroma a single aroma, continuously as long as the device is activated. This causes saturation of the olfactory senses and the perceived fragrance declines. Also, aerosol cans and pump sprays may produce large droplets which do not vaporize well and tend to rapidly fall under gravity and settle, also resulting in a continuous or lingering aroma which may degrade with time. Other devices, such as solid evaporative devices, experience a decay in aroma delivery rate over time.
U.S. Pat. No. 5,196,171 to Peltier describes the generation of vapors and/or aerosols by applying a DC voltage to a wick-like, porous emitter. In this case, the wick comprises a porous “capillament assembly” in which is disposed a central conductive electrode. In operation, the liquid provides a means of conducting the charge from the center of the wick to the outer surface where vaporization takes place due to corona discharge. The greatest concentration of vapors is created at the corners and edges (points or sharp radius edges) where the corona discharge forms.
Aerosols may also be created by the application of electrohydrodynamic (“EHD”) forces to a liquid. In doing so, the liquid forms a so-called Taylor cone at the EHD comminution site, becomes charged, and forms a jet or ligament which separates, or comminutes, into an aerosol. In utilizing EHD, it is desirable to keep voltages low to avoid corona discharge which is detrimental to the formation of aerosols. U.S. Pat. No. 5,337,963 to Noakes describes a spraying device which comprises a vertically-disposed capillary tube with one end immersed in a fragrance-producing oil. When an electrical potential is applied to the bulk liquid, generally near the submerged end of the capillary, the liquid is sprayed from the top end as a plurality of ligaments which break up into droplets. The applied electrical potential is reported to be in the range of 10-25 kV and must be high enough to cause EHD comminution at the top of the capillary. Liquid is fed by capillary action from a reservoir to the top end of the capillary for aerosolization. U.S. Pat. No. 5,503,335 to Noakes describes a similar spraying device, but which comprises a wick in place of the aforementioned capillary tube. The wick is fabricated from material having an open-celled structure. In this case as well, the high voltage is applied to the bulk liquid, generally near the submerged end of the wick. U.S. Pat. No. 5,810,265 to Cornelius et al. describes yet another similar spraying device, but which capillary structure comprises a hollow capillary tube having a convoluted inner surface to enhance capillary action. Similarly, the high voltage is applied to the bulk liquid, also generally near the submerged end of the capillary tube. Finally, U.S. Pat. No. 5,655,517 to Coffee describes a device for dispensing a comminuted liquid comprising a comminution site provided by fibers formed into a bundle projecting from an end surface or edge.
In the delivery devices described above, it is difficult to consistently and precisely control delivery of the spray. While EHD spraying offers many advantages, including the ability to produce consistent sprays of aerosol particles having a narrowly-tailored size distribution, significant inconsistencies were observed in the delivery rate of the liquid to the surrounding air.
It is, therefore, an object of the present invention to provide an aerosol delivery device that avoids or at least reduces adverse effects on an aroma resulting from the manner in which the aroma is delivered. It is another object of the present invention to provide an aerosol delivery device that enables improved control of delivery rate of the aerosol. It is yet another object of the invention to provide an aerosol delivery device that offers consistent aerosol delivery over the reservoir volume. It is a further object of the present invention to provide a method that offers the advantages of reduced adverse effects on the aroma, consistent aerosol delivery of the aroma, and improved capability for rapid vaporization.
It is a further object of the present invention to provide a device and method for delivering other formulations that benefit from dispersion as an aerosol. These include, for example, anti-microbial agents; insect repellants; attractants; sterilizers; confusants; pheromones; fumigants; odor neutralizers; therapeutic agents, such as menthol and eucalyptus; animal mood control agents; household cleaning products, such as surface cleaning agents, surface modification agents for aesthetic benefits, surface protection agents, and sanitization/disinfectant agents; household laundry care products, such as stain-removing agents, fabric fresheners, and other fabric treatment agents for aesthetic benefits; personal cosmetic care products for body cleaning, body lotion, and sunscreen products for humans; and consumer adhesives. Formulations, especially for aromas, are oil-based, but other carriers may be used such as water, polymers, or organic solvents.